


US! Sans x Reader: I am an Adult, Ya Know?

by KayDaKay



Category: Undertale (Video Game)
Genre: Best Friends, F/M, Fluff, Love, Monsters, Perversion, Protectiveness, Smut, Soul Bond, You thought I was innocent?
Language: English
Status: Completed
Published: 2019-01-06
Updated: 2019-01-06
Packaged: 2019-10-05 17:17:58
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,010
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17329193
Author URL: https://archiveofourown.org/users/KayDaKay/pseuds/KayDaKay
Summary: You and Sans have been best friends for a while.  The both of you immediately felt something for each other at first sight, but, what happens when an playful accident leads more?





	US! Sans x Reader: I am an Adult, Ya Know?

**Author's Note:**

> This is a smut. If you do not like them, then, I would advise you NOT to read this. The author is a pervert, and enjoys materials like this. LoL

The day started out normal. It was a typical day with the two Skeleton Brothers; Blue and Orange. How you met was very interesting, to say the least. After the monsters came out from the Underground, they slowly integrated with the human society. Generally, there were still some people who were racist against them, but usually the activist for monster rights beat them down (in a metaphorical sense- not violent). It just so happens that you were venturing out to different stores, when, you happened to find yourself in an all monster establishment. The stares from all the shoppers there burned into you as you awkwardly strolled through the aisles. 

Why didn’t you leave? Well, it might seem weird for a human to walk in to just turn around from seeing a dominant population of a different species. You try clearing your mind of the stares from monsters who were in awe. Picking up a Taco Kit, you observed the object in your hand while humming out, “Tacos don’t sound too bad? … I just can’t read Monster… Wait, how did Monsters figure out how to speak English anyways?!” You mumbled to yourself. When a deep voice suddenly chirped out, “MAGICCCCC!!!” Yelping, you jumped in the air dropping your possible dinner to the ground. Grasping at your chest, your breath came out in harsh pants as you tried calming your galloping heart. Looking around, you tried to find the culprit of the voice when something tugged at the hem of your shirt- “DOWN HERE HUMAN!” The same voice shouted happily, trying to capture your attention. Your eyes lowered to find an adorable, skeleton monster looking up at you the starry eyes.   
His outfit was… Interesting to say the least. He wore black pants which bunched up at the cuff of his boots. The little guy wore a baby blue shirt, and the same colored scarf tied around his neck. My god, he was just the cutest! A light blush dusted your cheeks, and a beautiful smile painted across your lips as you knelt to his size. The little monster seemed stunned for a minute, as a light blue blush dusted his own cheek bones. If possible, it seemed his Starry eyes widened even more. “Hey, little guy, what’s your name~?” You giggled out with adoring eyes. He seemed to choke on his own breath as he tried to splutter out an answer. “I-I’m not-!” He tried to squeak out until another masculine voice cut him off. “He’s not a ‘little guy’, miss. Well, not in the sense that you are thinking about, nyeh heh heh. “The stranger stated in a lazy drawl. 

Tilting your head up, your eyes almost bugged out as you were met with the sight of a giant skeleton monster in an orange hoodie. Rising to your feet quickly, you dust yourself off while chuckling nervously. “I apologize, is this your little brother?” You questioned hesitantly. A huff of annoyance puffed out of the smaller skeleton monster as the other one laughed heartily holding his sides. You watched in confusion as the little cutie started lecturing the bigger guy. “PAPYRUS! THIS ISN’T FUNNY, STOP LAUGHING!” The cutie yelled while flailing his arms about in anger. The giant known as ‘Papyrus’, wiped at the corners of his eye sockets (His tears were orange?!), and chuckled, “You’re right, bro. That joke was short coming, huh?” This sent the cutie into another fit shouting something about, ‘DON’T BORE THE HUMAN WITH YOUR SILLY PUNS!’ Papyrus just snickered at his own joke and at his brother’s annoyance.   
“Umm,” You started in a small voice, catching both brother’s attentions, “A-Aren’t you the older brother?” You asked the larger guy in confusion. The cutie’s jaw dropped in horror as Papyrus started laughing even harder holding his ribs. “N-NO, I AM THE OLDER BROTHER! ME, THE MAGNIFICENT SANS!!” the cutie shouted in embarrassment. Your face flushed red in your own shame and immediately began to apologize, “Oh my god, that was so rude of me to assume- you are just so adorable, that I thought… I’m so sorry!” Your squeaked out as your eyes shifted to him then to anywhere else. ‘Sans’ closed his eyes and cleared his throat, trying to calm himself down as he noticed the attention being drawn to them. Papyrus easily sent them a glare as they all scattered in different directions. “IT’S… IT’S OKAY, HUMAN.” You sighed in relief before being cut off by him again, “IF- “Your eyes shot open in fear, ‘there was an if?!’ He peeked one eye socket open to look at you, “IF, YOU BECOME MY FRIEND!” He chirped out. 

Blinking in shock you stared at him in surprise, ‘He wanted to be your friend?’ Fiddling with your hands, you stuttered out (to make sure you were hearing right), “Y-you really want to be friends?” Sans’ natural grin seemed to widen as he nodded in joy. “OF COURSE! YOU ARE SO NICE AND PRETTY, HUMAN! WHY WOULDN’T I?” He happily stated. You seemed to be startled at his outburst, but, it quickly changed into a grin of your own. “Y-yeah! We can be friends, my name is (Y/n)!” You introduced energetically, sticking your hand out to the smaller monster before you. He gripped it just as eagerly, shaking it up and down in a warm gesture. Both you stood there smiling dumbly at each other as Papyrus lazily watched the transaction unravel in front of him.  
That was how you met them and many more Monsters who quickly became family to you. Anyways, it has been a year since that fateful day, and all your friends and yourself were meeting at the park for a celebration of the anniversary for the Monsters. It has been five years since the Monsters have been freed from the Underground. A sunny, beautiful day at the park seemed to be the perfect setting for such an occasion. As you approached the site, the first person you saw was Asgore. He was someone who helped you adjust to Monster culture quickly. Asgore is the king of the Monsters who was gentle, loving, and full of puns. As the king, he wielded powerful fire-magic, you eventually learned. The king had taken you under his wing almost immediately saying, ‘All I need to know about you reflects in your soul’. He gave a small wave with a kind smile as he noticed you. His queen was named, Toriel, but the both seem to have marital problems that was secretly explained to you by Alphys. Speaking of Alphys, she immediately spotted you out of the corner of her eye and ran towards you.

“Hey there, loser!” She shouted with mirth, quickly drawing the attention of the other monsters attending. One of the monsters was your best friend, Sans. His grin instantly widens as usual as he and Alphys ran to you excitedly. The both were coming in fast and seemed as though they were not stopping anytime soon. Sweat rolled down your temples as your nervously watch the pair racing aggressively one shouting, ‘LOSER!’ and the other shouting ‘HUMAN!’ You loved both dearly, but, it appears you came at a wrong time since they both were just sparring for ‘fun’. The energy in their systems seemed to excite them too much as the eagerness in their face gave away enough information to know- you was gonna get an owie. Clenching your eyes shut, you braced for impact, until a pair of arms wrapped around your torso and yanked you out of the way. A crash echoed throughout the park as you peek an eye open at your savior. 

There stood the laziest Monster of all, Papyrus. He snickered at the dog pile the two of them made; both groaning in pain from the force of impact. The taller skeleton monster had one arm wrapped around you safely while the other held a cigarette to his mouth. Once your eyes landed on the cancer stick, you swatted him away hissing, “You know that stuff is terrible for your health, right?” He just chuckled letting you go, “Hey, it’s no skin off my bones- nyeh heh heh!” A groan comes from Sans as he shoots up from the ground. “PAPYRUS! DON’T RUIN THIS WONDERFUL DAY WITH YOUR TERRIBLE PUNS!” The smaller skeleton lectured storming up to the two of you. He picks you up suddenly causing a squeak to be ripped from your throat, “ESPECIALLY AROUND THE HUMAN!”   
Finally, his attention turned to you. His features almost seemed to soften before he was grinning again. Looking at him curiously, you let out a yelp as he spun you around in his arms. “SANS! YOU LET ME DOWN THIS INSTANCE!” You screeched feeling the world spin around you. “MWEH HEH HEH HEH! AND WHY WOULD THE MAGINIFCENT SANS DO THAT?!” He laughed out. You groaned from the churning of your stomach while answering him, “Unless the ‘Magnificent Sans’ wants vomit of his awesome shirt.” This made him quickly put you down but reached out for you again when he saw you stumbling about. “MWEH HEH, SORRY!” He nervously chuckled making sure you had your balance. Everyone around you two just laughed, shaking their heads at the silly antics. 

After your little reunion, all monsters (and you) settled down to eat and talk. Alphys and Undyne sat by each other, the lizard monster had one buff arm wrapped around her girlfriend lovingly as the fish monster shyly snuggled closer to her. Asgore and Papyrus were shooting off puns at each other while letting out bellows of laughter whenever the other made a good one; Everything was just perfect.You sat back and watched all of them with affection and serenity. That is, until Sans tugged on your shirt. Glancing down, you find him smiling up at you with just the same amount of affection. With a small smile, you rubbed the top of his skull soothingly as the smaller monster purred at the attention. Then, you heard the giggling- looking up, you noticed most monsters watching you both with a knowing look. This seem to both fluster and confuse you as they turned away to speak about the scene you two made. You turned to Sans to see if he was just as confused as you were, but he just affectionately snuggled your arm with a sigh of content. Blushing, you scratched your cheek awkwardly as you realized what the monsters could be giggling about. You didn’t care, though, Sans always made you feel loved. Since you first met him, you always held him close to your heart. It just seems your chest tightened when your eyes met, and a fluttering feeling tickled from deep with inside yourself. 

The sun burnt the sky in shades of orange and pink signaling the coming of the night. Gathering all your stuff, you waited for your friends to catch up. Your eyes were turned to the sky as you watched a flock of birds fly off in the distance; only black crescents in the sky. Once again, Alphys and Sans were rough housing again too close near you, but you weren’t paying attention. Your mind was clouded with thoughts of today unaware of the pair wrestling too close to you. When your thoughts finally turned to the topic of your feelings about Sans, you were violently pulled out of them when a solid object slammed into you causing you to twist and turn in the air. With a resounding thud, you slammed face first into whatever sent you flying in the first place.   
The first thing you noticed that your lips were pressed harshly into something hard, but malleable. It could be that you were kissing the ground, but, you felt something squirming beneath you. The thing struggled for a little bit before becoming very still. Humming in mixture of pain and confusion, your eyes slowly open to reveal the thing underneath you. With a squeak of surprise, you ripped your lips off your shell-shocked friend. The others ran over shouting words of concern, but, you couldn’t tell what they were saying due to the buzzing in your ears. Your mouth was dry as your jaw dropped in total astonishment. 

Here you thought, Sans would have a childish reaction to an accidental kiss by his best friend, but- it was the exact opposite. His once starry eyes shifted into baby blue hearts, his whole skull was a deep blue, but that wasn’t the thing that surprised and scared you. He seemed love drunk off the short kiss. Drool seemed to drip from his open mouth as he panted like a dog in heat. Your lip quivered in anxiety and excitement as the smaller monster made no movements. He just laid there, seeming to anticipate the next thing you would throw at him.   
When you made no advances, your best friend squirmed and whined underneath you that produced a wave of arousal to flood your lower regions. Sitting up quickly, you crawled away from him releasing a whimper of your own. You could feel his scorching stare on your crawling figure and could’ve sworn you heard a groan of appreciation. “Sans, (Y/n)- are you two okay?!” Papyrus swooped in on the two of you like a worried hen. You could only breathe heavily, willing your arousal to disappear. It burned, oh my god did it burn! This guy, your best friend, left you desperate and needy over a little kiss! If you are feeling like this, then, by the judgement of his face earlier- he must be feeling it worse. Turning to look at Sans with concern, you were only found floored as he calmly stood up with his usual grin. “THE MAGNIFICENT SANS IS OKAY!” He cheered at the top of his lungs, brushing off the dirt from his pants. Papyrus sighed in relief and hugged his brother close to his chest; mumbling about how he really rattles his bones, sometimes. This caused Sans to go into another one of his tantrums over his baby brother’s ‘terrible’ puns. When everyone was assured the both of you were okay, they quickly dismissed to their rides eager to go home. 

Alphys immediately apologized to you with an upset Undyne right behind her. “N-no, really, it’s okay! I am fine.” You tried reassuring the both with a small smile. It seemed to do the trick as Alphys let out a laugh and ruffled your hair. Your smile was weak with exhaustion from the sudden turn of events, but, you harbor no ill feelings towards your lizard friend. The couple waved good bye at you with a promise to see you soon before entering their car and drove off. You sighed deciding it was also your turn to leave. 

However, as you turned around, you were met with the sight of your best friend. His smile seemed different, and those hearts had returned to his sockets. A little giggle escaped him as it looked like he was vibrating in place. This caused you to become a little concerned as a nervous smile painted itself on your lips. “S-Sans, you okay? I must’ve really swept you off your feet back there?” You giggled at your own pun. Yet, he remained the same; no lecturing, no nothing. This was DEFINITELY a cause for concern as you knelt to him. “Buddy? Did I hurt you?” You cooed to him. Again, he seemed to shiver at your tone and his hands twitched by his side. 

Then, with the speed of lighting, the smaller monster snatched your face into his hands and brought your lips harshly to his teeth. ‘Mmmmmmm?!’ you screeched in a muffled tone just as he moaned in a deep, lusty voice. His gloved fingers curled into your jaw, trying to pull you impossibly closer. Almost as if he was trying to morph you both together! Suddenly, something slimy pressed against your bottom lip causing you heart to thud in your ears. It was an accident (really it was!), but a gasp escaped you as he took that to his advantage. A long, slimy appendage shot into your mouth and swirled its around his new-found territory. You couldn’t help but groan as that thing wrapped around your human tongue and began to massage the smaller muscle. Quickly, the fire of arousal scorched your entire being, sending your rational thinking into flames. All you could think about was the throbbing in your lower regions and how you would do anything to satisfy it. He watched you with the same drunken look from earlier- almost as if he were in bliss. Then, you felt him rut something hard into your abdomen. When it dawns on you what exactly that ‘hard’ thing was, you could feel yourself dripping with need. Clenching your eyes shut from the intense feeling, you let out a needy whine and ran your fingers down your thighs towards the place you needed him most.  
To others, it may have looked awkward for a human to be kneeling on the ground while a small, skeleton monster fucks her mouth with his tongue, but hey, what can you do? 

“Sans! It’s time to go!” Papyrus’ voice snaps the both of you out of your trance. Your ‘best friend’ pulls away with a mixture of saliva stringing from your lips to his teeth. He blinks twice before the hearts turned back to stars. With a giggle he winks flirtatiously at you, “I usually don’t like sweets, buuuut I think you’re the one dessert I would beg for. ” He whispers lowly letting out a dark chuckle sending a cold chill down your spine. And, just like a switch, he turns to his brother and shouts, “COMING PAPPY!!!” Another smirk shot your way before he ran up to the car. You watched, gawking in astonishment as the little guy rolled his window down and blew you a kiss as the vehicle veered off to the main road…….. Just what kind of darkness does this guy have in him?


End file.
